cpu/stm32/periph_pwm: add doc for complementary timer channels

gschorcht · gschorcht · commit d8cf5a0c66ae · 2023-05-19T16:51:26.000+02:00
diff --git a/cpu/stm32/include/periph/cpu_pwm.h b/cpu/stm32/include/periph/cpu_pwm.h
@@ -33,10 +33,21 @@ extern "C" {
 
 /**
  * @brief   PWM channel
+ *
+ * When using a general-purpose timer for a PWM device, the outputs OC<n> of
+ * each of the four capture/compare channels can be used as PWM channel.
+ * The respective capture/compare channel is then specified with 0...3 in
+ * `cc_chan` for the outputs OC1...OC4.
+ *
+ * Advanced timers like TIM1 and TIM8 have additionally three complementary
+ * outputs OC<n>N of the capture/compare channels, which can also be used
+ * as PWM channels. These complementary outputs are defined with an offset
+ * of 4, i.e. they are specified in `cc_chan` with 4...6 for OC1N...OC3N.
  */
 typedef struct {
     gpio_t pin;             /**< GPIO pin mapped to this channel */
-    uint8_t cc_chan;        /**< capture compare channel used */
+    uint8_t cc_chan;        /**< Capture/compare channel used: 0..3 for OC1..OC4
+                                 or 4..6 for OC1N..OC3N for advanced timers */
 } pwm_chan_t;
 
 /**
